It is known to crack or thermally dehydrochlorinate 1,1,2-trichloroethane to obtain 1,1-dichloroethylene (vinylidene chloride) and an isomeric mixture of cis- and trans-1,2-dichloroethylenes. Vinylidene chloride may be either polymerized to produce polyvinylidene chloride resin or may be catalytically hydrochlorinated to produce methylchloroform, a commonly used degreasing solvent. Since the 1,2-dichloroethylene isomers are of considerably less value, the vapor phase reaction is typically conducted in the presence of catalysts which selectively favor the formation of vinylidene chloride.
U.S. Pat. No. 3,870,762 discloses dehydrochlorinating 1,1,2-trichloroethane in the presence of a chloride or fluoride of potassium, cesium or rubidium carried on a silica support of a type known as Porasil.RTM.. Copending, commonly assigned application Ser. No. 744,564, filed Nov. 24, 1976, discloses a vinylidene chloride selective catalyst comprising cesium halide, preferably cesium chloride, supported on humidified, high surface area silica gel.
A catalyst has been found which gives improved selectivity to vinylidene chloride in the vapor phase dehydrochlorination of 1,1,2-trichloroethane, especially when the vapor phase reaction is conducted at super-atmospheric pressure.